Multiple focus eyeglasses have been in common use for many years. The most prevalent version of multiple focus eyeglasses are bifocals in which one or both lenses include distinct regions providing vision corrections for forming focused images of objects at two distinct locations. In a typical bifocal lens, a first region provides a vision correction so that distant objects are observed in focus. In a second region of the bifocal lens, a different correcting region is-provided for viewing near images, for example, during reading. Eyeglasses with multiple focus lenses are handy because objects at different distances can be viewed in focus using the different correcting regions of the lenses without changing between separate pairs of distant-vision and near-vision eyeglasses.
Although, in many instances, bifocals can be particularly useful, in some situations they can present an impediment to achieving some visual goal. Typically, the near-vision correction for reading is at the lower part of the lens and when it is desired to view a distant object looking downward, i.e., through the near-vision correcting region of the lens, some physical adjustment in head or eye position must be made in order to see the desired object in focus. Thus, certain activities, such as hunting and golfing, present dilemmas for those persons who wear bifocal lenses. For example, in hunting, when it is desired to view a distant target along a gun sight, the near-vision part of the bifocal lens is typically in the line of vision preventing accurate sighting. In golfing, when preparing to hit a teed ball or when taking other strokes, it is desirable to keep the head down. In that posture, it is difficult or impossible to view the ball through the distant-vision part of bifocal and, therefore, a golfer wearing bifocals has a tendency to change head position before and during his swing with a detrimental effect on the drive.
One solution to the problem of attempting to view distant objects through the near correction region of a bifocal lens, other than adjusting the head position, is the provision of two pairs of glasses, one for near-vision viewing and one for distant-vision viewing. However, in activities such as golfing and hunting, it is necessary to carry out some activities while viewing near objects, e.g., selecting a club, inspecting a ball, and the like, or loading ammunition, cleaning a firearm or the like, and other activities while viewing distant objects, making repeated glasses changing a nuisance. Moreover, carrying of an additional pair or pairs of glasses can be annoying during sporting activities.
Accordingly, it is desirable to provide some way of switching between conventional bifocal vision and distant-vision over all of an eyeglass lens viewing area without the necessity of changing glasses.